| With Fuji apple materials,Lactobacillus paracasei 20241,Bifidobacterium animalis6165,Streptococcus thermophilus 6063 and Lactobacillus acidophilus 6005 were chosen to be the main zymophyte for the fermentation of apple juice.The results provide a practical basis for the research and application of lactic acid bacteria in fermented fruit and vegetable juice.The main results were described as follows.(1)Using viable count and sensory evaluation as the main indices,single-factor analysis was conducted to measure the effects of fermentation temperature,ratio of probiotics strains,inoculation,fermentation time on the viable count and sensory evaluation.Combining single-factor experiment results and practice,ratio of probiotics strains,inoculation and fermentation time were further researched using a Central-Composite design to optimize the fermentation conditions.When the fermentation temperature was selected as 37?,the best main fermentation technology parameters were determined by response surface experiment and they were as follows:ratio of probiotics strains of 1:1:1:1,inoculation of 2%and fermentation time of 24h.Under these conditions viable count was 19.85×10~7CFU/mL and sensory score reached 80.23.(2)Using the best conditions to ferment apple juice,the OD value,total sugar,total phenol,organic acids and polyphenols were determined and monitored during the mixed fermentation of lactic acid bacteria in apple juice by ultraviolet spectrophotometer,Fehling Reagent Titration,Folin-Ciocaileu and HPLC.The results showed that the OD value was on the rise,and total sugar had a downward trend,besides,the total phenol were in a dynamic change.The content of malic acid and succinic acid decreased significantly after fermentation(p<0.05),but lactic acid,quinic acid,citric acid,tartaric acid,pyruvic acid and shikimic acid content were significantly improved(p<0.05).The content of catechins,root peel glucoside,quercetin,epicatechin and vanillic acid had increased,while chlorogenic acid,gallic acid,caffeic acid,p-coumaric acid,ferulic acid,rutin and cinnamic acid had significantly reduced(p<0.05).In the process of the mixed fermentation of lactic acid bacteria in apple juice,organic acids and polyphenols were affected by different degrees,so they still changed consistently in the whole process.(3)Single lactic acid bacteria strain fermentation and mixed-strains fermentation of apple juice were conducted,respectively.The OD value during fermentation was monitored by UV-Vis spectrophotometer.The aroma components of 9 fermented apple juice was identified by head-space solid phase micro-extraction(HS-SPME)combined with gas chromatography-mass spectrometry(GC-MS),and they were analyzed with threshold of different aroma components and aroma value.Sensory evaluation was also carried out on the fermented apple juice.The results showed that the OD value of apple juice increased logarithmically with time.Forty eight aroma components were identified from 9 fermented apple juice,including alcohols,esters,aldehydes,ketones and phenols The esters were the most abundant components and had the largest number of types,followed by alcohols.In addition,according to the aroma value,butyric acid ethyl ester,ethyl-2-methylbutyrate,2-methylbutyl acetate and hexyl acetate were the main aroma components and had outstanding contribution to the 9 fermented apple juice.The content of aroma components and aroma value in single-strain fermentation and mixed-strain fermentation of apple juice were significantly different(P<0.05).It was shown that the total contents of alcohols,esters and other kinds of aroma components with mixed-strain fermentation were significantly higher than those of single-strain fermentation and they gave the apple juice stronger fruity,green and flowery aroma.Overall,the sensory score of the mixed-strain fermentation was higher than that of the single-strain fermentation.A ratio of 1:1:1:1 was the optimal strain combination in sensory acceptance. |
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